In conventional X-ray CT apparatuses, when a scan region the size and position of which change is scanned, a scan range is set large. In the conventional X-ray CT apparatuses, a scan ends based on an instruction input by a user who has confirmed that the entire scan region has been scanned.
However, the scan region the size and position of which change sometimes does not fit within the scan range set large. In this case, in the conventional X-ray CT apparatuses, a part of the scan region that has not fit within the scan range and a periphery thereof are additionally scanned. In the conventional X-ray CT apparatuses, three dimensional CT image data including a joint is sometimes generated since the size and position of the scan region are not necessarily same as those in the previous scan time.
In conventional X-ray CT apparatuses, even when the scan region is within the scan range set large, if a moving speed of a tabletop is fast, unnecessary range is sometimes scanned until the user inputs an instruction of making the scan ends.